Recycled rubber processing and performance enhancement

Abstract

A process for reclaiming sulfur-cured, vulcanized rubber by combining finely ground scrap vulcanized rubber within a specialized, twin-screw extruder capable of providing strong shearing and just-on-time mixing; adding a reclaiming agent to the extruder; and masticating the rubber scrap and reclaiming agent within the extruder until the rubber scrap is devulcanized. The present invention also discloses a unique composition of reclaiming agent, which preferably includes the following compounds: accelerators TBBS, ZMBT, MBT, and TMTM; activators zinc oxide and stearic acid; and zinc salts of fatty acids and sulfur. The reclaimed rubber is suitable for use in producing high-grade, rubber products without adding a binder, or for combining with fresh rubber compounds to produce high-specification rubber products.

What is claimed is:  
     
       1. A chemical composition for obtaining curable elastomeric material from sulfur-cured elastomeric material having a vulcanized network, comprising: 
       (a) a sulphenamide group accelerator selected from the group consisting of:  
       (i) N-cyclohexyl-2-benzothiazole sulphenamide (CBS);  
       (ii) benzothiazyl-2-morpholine sulphenamide (MBS);  
       (iii) N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (iv) 2-(N-morpholinyldithio)-benzothiazole, and  
       (v) morpholinyl-thiocarbonylsulphene morpholide;  
       (b) at least two mercapto group accelerators selected from the group consisting of:  
       (i) zinc 2-mercapto benzothiazole (ZMBT);  
       (ii) 2-mercaptobenzothiazole (MBT), and  
       (iii) dibenzothiazyl-disulphide (MBTS);  
       (c) a thiuram group accelerator selected from the group consisting of:  
       (i) tetramethylthiuramic monosulphide (TMTM);  
       (ii) tetraethylthiuram disulphide (TETD);  
       (iii) tetramethylthiuram disulphide (TMTD), and  
       (iv) tetrabenzylthiuram disulphide (TBTD);  
       (d) zinc salts of fatty acids;  
       (e) at least one activator selected from the group consisting of:  
       (i) stearic acid;  
       (ii) methacrylic acid, and  
       (iii) zinc oxide, and  
       (f) sulfur.  
     
     
       2. The chemical composition of  claim 1 , wherein: 
       such sulphenamide group accelerator is N-tert-butyl-2-benzothiazole sulphenamide (TBBS).  
     
     
       3. The chemical composition of  claim 1 , wherein: 
       such mercapto group accelerators are zinc 2-mercapto benzothiazole (ZMBT) and 2-mercaptobenzothiazole (MBT).  
     
     
       4. The chemical composition of  claim 1 , wherein: 
       such thiuram group accelerator is tetramethylthiuramic monosulphide (TMTM).  
     
     
       5. The chemical composition of  claim 1 , wherein: 
       such activator is stearic acid and zinc oxide.  
     
     
       6. The chemical composition of  claim 1 , wherein the composition comprises: 
       (a) about 4% to about 10% by weight N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (b) about 4% to about 18% by weight zinc 2-mercapto benzothiazole (ZMBT);  
       (c) about 4% to about 18% by weight 2-mercaptobenzothiazole (MBT);  
       (d) about 3% to about 5% by weight tetramethylthiuramic monosulphide (TMTM);  
       (e) about 3% to about 6% by weight zinc salts of fatty acids;  
       (f) about 1% to about 3% by weight stearic acid;  
       (g) about 1% to about 3% by weight zinc oxide, and  
       (f) about 40% to about 65% by weight sulfur.  
     
     
       7. The chemical composition of  claim 6 , wherein the composition comprises: 
       (a) about 6% by weight N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (b) about 16% by weight zinc 2-mercapto benzothiazole (ZMBT);  
       (c) about 8% by weight 2-mercaptobenzothiazole (MBT);  
       (d) about 4% by weight tetramethylthiuramic monosulphide (TMTM);  
       (e) about 4% by weight zinc salts of fatty acids;  
       (f) about 2% by weight stearic acid;  
       (g) about 2% by weight zinc oxide, and  
       (f) about 58% by weight sulfur.  
     
     
       8. The chemical composition of  claim 1 , in which, the sulfur-cured elastomeric material having a vulcanized network is selected from the group consisting of: 
       (a) natural rubber (NR);  
       (b) polybutadiene (BR);  
       (c) styrenebutadiene (SBR);  
       (d) ethylene-propylene-diene-terpolymer (EPDM);  
       (e) neoprene (CR);  
       (f) nitrile (NBR), and  
       (g) combinations of the above.  
     
     
       9. A process for obtaining curable elastomeric material from sulfur-cured elastomeric material having a vulcanized network, such curable elastomeric material being capable of being recompounded and recurred into useful elastomeric products, such process comprising: 
       (A) reducing such sulfur cured elastomeric material to fine particle crumbs;  
       (B) providing a twin screw extruder for processing such crumb;  
       (C) treating such crumb, by means of such twin screw extruder, with an admixture comprising:  
       (a) a sulphenamide group accelerator selected from the group consisting of:  
       (i) N-cyclohexyl-2-benzothiazole sulphenamide (CBS);  
       (ii) benzothiazyl-2-morpholine sulphenamide (MBS);  
       (iii) N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (iv) 2-(N-morpholinyldithio)-benzothiazole, and  
       (v) morpholinyl-thiocarbonylsulphene morpholide;  
       (b) at least two mercapto group accelerators selected from the group consisting of:  
       (i) zinc 2-mercapto benzothiazole (ZMBT);  
       (ii) 2-mercaptobenzothiazole (MBT), and  
       (iii) dibenzothiazyl-disulphide (MBTS);  
       (c) a thiuram group accelerator selected from the group consisting of:  
       (i) tetramethylthiuramic monosulphide (TMTM);  
       (ii) tetraethylthiuram disulphide (TETD);  
       (iii) tetramethylthiuram disulphide (TMTD), and  
       (iv) tetrabenzylthiuram disulphide (TBTD);  
       (d) zinc salts of fatty acids;  
       (e) at least one activator selected from the group consisting of:  
       (i) stearic acid;  
       (ii) methacrylic acid, and  
       (iii) zinc oxide, and  
       (f) sulfur, and  
       (D) working such crumb and such admixture in such extruder for a sufficient time, at a selected temperature to break sulfur cross links within such sulfur cured elastomeric material.  
     
     
       10. The process as specified in  claim 9 , wherein the ratio of crumb to admixture comprises: 
       about 100 parts crumb, and  
       between about 1 to 2 parts admixture.  
     
     
       11. The process as specified in  claim 9 , wherein 
       the working time is less than about two minutes.  
     
     
       12. The process as specified in  claim 9 , wherein 
       the temperature for working such crumb and such admixture is selected between about 75° C. and 85° C.  
     
     
       13. The process as specified in  claim 9 , wherein such admixture comprises: 
       (a) about 4% to about 10% by weight N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (b) about 4% to about 18% by weight zinc 2-mercapto benzothiazole (ZMBT);  
       (c) about 4% to about 18% by weight 2-mercaptobenzothiazole (MBT);  
       (d) about 3% to about 5% by weight tetramethylthiuramic monosulphide (TMTM);  
       (e) about 3% to about 6% by weight zinc salts of fatty acids;  
       (f) about 1% to about 3% by weight stearic acid;  
       (g) about 1% to about 3% by weight zinc oxide, and  
       (f) about 40% to about 65% by weight sulfur.  
     
     
       14. The process as specified in  claim 11 , wherein such admixture comprises 
       (a) about 6% by weight N-tert-butyl-2-benzothiazole sulphenamide (TBBS);  
       (b) about 16% by weight zinc 2-mercapto benzothiazole (ZMBT);  
       (c) about 8%. by weight 2-mercaptobenzothiazole (MBT);  
       (d) about 4% by weight tetramethylthiuramic monosulphide (TMTM);  
       (e) about 4% by weight zinc salts of fatty acids;  
       (f) about 2% by weight stearic acid;  
       (g) about 2% by weight zinc oxide, and  
       (f) about 58% by weight sulfur.  
     
     
       15. The process as specified in  claim 9 , wherein the sulfur-cured elastomeric material having a vulcanized network is selected from the group consisting of: 
       (a) natural rubber (NR);  
       (b) polybutadiene (BR);  
       (c) styrenebutadiene (SBR);  
       (d) ethylene-propylene-diene-terpolymer (EPDM);  
       (e) neoprene (CR);  
       (f) nitrile (NBR), and  
       (g) combinations of the above.